1. Field of the Invention
The present invention relates to a rangefinder apparatus for use in AF (Auto Focus) cameras and video cameras, etc.
2. Related Background Art
As a rangefinding system for rangefinder apparatus used in AF (Auto Focus) cameras and video cameras, a so-called passive rangefinding scheme which makes it possible to measure distances ranging from a short distance to a long distance if an object image has a certain degree of brightness and contrast has conventionally been known in general.
In the passive rangefinding scheme, correlation is calculated according to output signals of a pair of light-receiving sensors on which a pair of object images are respectively formed by external light from an object, and the distance to the object is calculated according to the smallest minimal value (peak value) exhibiting the highest degree of correlation in the correlation values obtained by the correlation calculation. For accurately calculating the distance to the object, the correlation calculation is usually carried out for each of a plurality of rangefinding areas into which the field of view of a camera is divided.
In general, in the passive rangefinding scheme, output signals from a pair of light-receiving sensors (line sensors) are accumulated (integrated), so as to generate a pair of sensor data, which are then A/D-converted and stored for the correlation calculation. Then, while a pair of windows as areas for reading out a pair of data used for the correlation calculation from the stored pair of sensor data are relatively shifted in succession, a pair of data are sequentially read out, and the correlation calculation is carried out. According to the amount of shift of windows corresponding to the smallest minimal value (local minimum value) (peak value) exhibiting the highest degree of correlation in the correlation values obtained by the correlation calculation, the distance to the object is calculated.
Known as a rangefinder apparatus of this kind of passive rangefinding scheme is one which, if the sensor data integrating the line sensor output signals include a region with a low luminance and low contrast luminance distribution when taking a picture against light or the background of a night scene, the output signals of line sensors are integrated again for the region with the low luminance and low contrast in order to enable the rangefinding for an object in this region (see, for example, Patent Document 1).
[Patent Document 1] Japanese Patent Application Laid-Open (Tokukai) No. 2001-141987